Yes, basically it is a digital temperature gauge connected to a relay. When the temperature falls below a set point it will allow electricity to pass through to the outlet. If your refrigerator or freezer is plugged into the outlet, it turns it on and allow it to turn on until it cools down to the set point, then it will disengage the relay preventing electricity from passing through. It's a very basic design.
You can make them if you are not in a hurry. BYO had an article in their magazine showing how to do it, but I'm certain you can find instructions online. Just look up STC-1000.